An aircraft will typically include one or more potable-water-using stations (e.g., sinks, basins, beverage makers, ice makers, etc.) and each station will usually include a drain line for graywater. Graywater is a specific form of waste fluid that is no longer suitable for drinking but does not include septic wastes (i.e., it does not interact with toilet water). Graywater can include, for example, unfinished beverages poured down sinks and/or hand-washing water from lavatories.
An aircraft will usually include some type of graywater ejection system. In certain aircrafts and/or in certain aircraft orientations, graywater can gravity drain to a drainmast. If gravity draining is not always possible and/or practical, graywater can be stored in a tank, and a discharge line can extend from this storage tank to a port on the aircraft's fuselage. When the aircraft is grounded, the port can be opened by airline personnel and the stored graywater discharged from tank and into an appropriate sewer.